Bovine serum albumin in aqueous guanidine hydrochloride solutions. Preferential and absolute interactions and comparison with other systems

Abstract

The partial specific volume, .hivin.v20, of bovine serum albumin at 25.degree. C was 0.728 .+-. 0.001 ml/g in solutions of guanidine hydrochloride (GuHCl), 0.01 M dithioerythritol (DTE), independent of GuHCl concentration (3-6 M). The volume decrease on denaturation is about 400 ml/mol (.hivin.v20 in H2O at the same temperature was 0.734). From the reduced density increments at constant chemical potential of diffusible solutes, the apparent volumes, .vphi.'', increased from 0.693 ml/g at 3 M GuHCl to about 0.725 ml/g at 7 M GuHCl. The phenomenological interaction parameter, .xi.3 (grams of GuHCl bound per gram of protein), decreased from about 0.2 at 3 M GuHCl to about 0.07 at 6.4 M GuHCl. The phenomenological interaction parameter, .xi.1 (grams of H2O bound per gram of protein), is negative and become less negative with increase in GuHCl concentration. The relation between .xi.3 and .xi.1 and physical binding and exclusion of low-molecular-weight components are discussed in terms of simple model consideration. Over the range of GuHCl concentrations studied about 0.2 g of H2O and 0.28 g of GuHCl are bound per gram of protein. This corresponds on the average to 1.3 molecules of H2O and 0.35 molecule of GuHCl per amino acid residue. Similar results were found by recalculating previous results for aldolase. These results on proteins in GuHCl solution are in marked contrast to the behavior of DNA at high concentrations of NaCl and CsCl, analyzed on the basis of earlier work.